phenomenon

galactic outflow acceleration

The process by which material is expelled from a galaxy's nucleus and accelerated, often involving cosmic rays and dust.
26 related articles · 2 formulas

Description

Galactic outflow acceleration is the process by which gas, dust, and cosmic rays are expelled from a galaxy's central regions and accelerated to high velocities, often forming large-scale winds that can extend far beyond the galactic disk. These outflows are typically driven by intense star formation, supernova explosions, or the activity of a supermassive black hole at the galaxy's core. The accelerated material can carry energy and heavy elements into the intergalactic medium, influencing the galaxy's evolution by removing gas that would otherwise form new stars and enriching the surrounding environment.

History

The concept of galactic outflows has been developed over several decades, with early observations in the 1960s and 1970s revealing gas moving at high velocities in the halos of galaxies. The role of cosmic rays in driving these outflows was proposed in the 1980s and has been refined through subsequent theoretical work and simulations.

How it works

The acceleration mechanism involves a combination of thermal pressure from supernova explosions, radiation pressure from hot young stars, and cosmic rays that couple to the gas via magnetic fields. Cosmic rays, being charged particles, can stream through the galaxy and transfer momentum to the surrounding gas through collisions and magnetic field interactions, effectively pushing the material outward. In the case of active galactic nuclei, relativistic jets and intense radiation from the accretion disk around the black hole can also drive outflows, accelerating material to speeds of hundreds to thousands of kilometers per second.

In practice

Understanding galactic outflow acceleration is crucial for modeling galaxy formation and evolution, as well as for interpreting observations of the circumgalactic medium in large-scale surveys.

Fun fact

Some galactic outflows are so powerful that they can eject material from the galaxy entirely, escaping into intergalactic space and carrying heavy elements over millions of light-years.

Concept graph →

Formulas

$$\dot{M}_{out} = \rho v A$$
Mass outflow rate is density times velocity times area.
What is in the formula
Ṁ_outvariableMass outflow rate — mass flow rate kilogram per second
ρvariableMass density of the outflowing material — mass density kilogram per cubic metre
vvariableFlow velocity perpendicular to the area — velocity metre per second
AvariableCross-sectional area through which material flows — area square metre
$$\dot{m}_{out}=ωn_hm_pv_{out}r$$ · 2606.05312v1
\dot{m}_{{out}}=1.2m_\odot{yr}^{-1}(\frac{ω}{0.4*4π})(\frac{r_{{out}}}{1{kpc}})(\frac{v_{{out}}}{200{km/s}})(\frac{ew}{1{å}}) · 2607.20606v1
$$v_{\rm term} \propto \dot{m}^{-1/2}$$
Terminal outflow velocity scales with accretion rate.
What is in the formula
v_{\rm term}variableTerminal outflow velocity — velocity metre per second
\dot{m}variableMass accretion rate — mass accretion rate kilogram per second
v_{\rmterm}=7.46*10^2(\dot{m}_3/2)^{-1/2}{\rmkms^{-1}} · 2607.17448v1

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